The invention relates to an electrical machine having a housing containing a rotor and a stator, with the rotor and/or the stator having at least one laminated core with a substantially rectangular cross section.
Iron cores are used in a very wide variety of types of electrical machines for conducting the magnetic flux with a low level of loss. In this case, inductively generated eddy currents, which lead to heating of the electrical machine and furthermore cannot be used, are produced under the influence of an alternating electrical field in iron cores comprising solid material. In order to minimize this, iron cores for electrical machines are preferably formed from metal sheets which are electrically insulated from one another or as cut strip-wound cores. In this case, the insulated metal sheets are either constructed as individual, loose metal sheets, also called laminations, or as an interconnected laminated core, also called stack of laminations, during assembly of the electrical machine.
As a result of the development of brushless DC motors with an air gap winding, the basic shape of the laminated cores with pole shoes has developed to form annular laminated cores which form a hollow-cylindrical body when they are stacked. These designs of laminated cores are used, for example, in electrical machines as disclosed by DE 10 2007 029 739 A1.
In order to produce the laminated cores, the individual metal sheets are punched out of a sheet metal strip, layered to form a laminated core and connected to one another. In this case, the metal sheets can be connected, inter alia, by baked enamel, punch-stacking or by a weld connection. A high proportion of waste is created particularly when punching metal sheets which produce a hollow cylinder when layered. In order to produce the laminated cores, the sheet metal part of the laminated core is punched out of a sheet metal strip with a width which is a few millimeters greater than the outside diameter of the sheet metal part which is to be punched. When the sheet metal part is punched out, both the inner part of the sheet metal part and the outer part of the sheet metal part, that is the remains of the sheet metal strip, are wasted. Therefore, in order to produce a laminated core with a weight of approximately 190 g with an outside diameter of 68 mm and an inside diameter of 64 mm and a thickness of 0.7 mm, approximately 2.2 kg of sheet metal are required in order to be able to produce the laminated core. This corresponds to over 90% waste.
In order to reduce waste, cut strip-wound cores are used in the case of transformers. To this end, a sheet metal strip is wound onto a mandrel with a rectangular cross section and adhesively bonded. The wound, adhesively bonded laminated core is then divided centrally parallel to the longitudinal axis of the laminated core and the separating surfaces are polished. Wound coils are inserted into the halves and adhesively bonded. As a result of the division of the cut strip-wound core in order to release it from the mandrel, two thin air gaps are produced when the two cut strip-wound core halves are joined to one another, said air gaps influencing the magnetic flux between the two cut strip-wound core halves. On account of the two-part design of the cut strip-wound core, said cut strip-wound core is particularly unsuitable for use in rotating electrical machines. The cut strip-wound core is primarily unsuitable for use on the rotor since the metal sheets are exposed to high centrifugal forces here. The air gap and the polishing steps required to minimize the air gap do not favor use on the stator. Therefore, laminated cores in which the individual metal sheets are produced by means of punching from a sheet metal strip are primarily used in electrical machines with a rotor and/or a stator.